Could “Hairy Roots” Become Biofactories?

by Jade Boyd

Mention the word biofactory, and you’re likely to envision a sterile lab filled with fancy glassware and expensive, arcane equipment. Think, instead, of a greenhouse filled with blue periwinkles.

Rice University bioengineers have reported an advance in modifying the immense potential of “hairy roots” as natural factories to produce medicines, food flavorings and other commercial products.
Hairy roots are a type of tumor that forms on plants infected by the soil bacterium Agrobacterium rhizogenes. By inserting a specific gene into the bacterium, researchers can integrate that gene into the host plant’s DNA. Eventually, the host develops a system of fuzzy-looking roots near the site of the infection. These so-called “hairy roots” are transgenic, meaning they contain the genes of both the host plant and the bacterium.

“The species of periwinkle that we’re studying produces a wide variety of alkaloids, including the anti-cancer drugs vincristine and vinblastine,” said study co-author Ka-Yiu San ’78, Rice’s E.D. Butcher Professor of Bioengineering and professor in chemical and biomolecular engineering. “Hairy roots have a number of advantages over cell cultures as a production platform for these compounds.”

Scientists believe they can create hairy roots that churn out the product of inserted genes with a stability and productivity not possible with most other plant cell cultures. San said scientists have long wanted to harness the production prowess of hairy roots for industry, but that first they must determine the long-term stability of the genetically altered roots.

In the new study, San and Rice graduate student Christie Peebles described the methods they used to keep a transgenic hairy root culture alive for 4 1/2 years. At the outset, they infected a periwinkle plant with a bacterium carrying a gene for fluorescence. By transferring root tips into fresh liquid every four weeks, they maintained a stable root culture that had the characteristic fluorescent glow produced by the gene.

Ultimately, San and his collaborators hope to make genetic modifications to the metabolic pathways of the transgenic periwinkle roots — changes that will allow them to produce far more vincristine and vinblastine than is normally produced by a regular periwinkle plant.

Study co-authors include Iowa State University’s Jacqueline Shanks, an adjunct professor of bioengineering at Rice, and plant biologist Susan Gibson of the University of Minnesota. The research is supported by the National Science Foundation, and the findings are available online in the November/December 2007 issue of the American Chemical Society’s bimonthly journal Biotechnology Progress.